Refining of crude coke oven light oil



Oct. 11, 1955 J. J. LAwToN REFINING OF CRUDE COKE OVEN LIGHT OIL Filed May 28, 1952 mDnImmd 22E Iv -mm Ll mv mtzn mw QZO IV nina o 55 NN mm IV mm 5.53 mm .vm motmm Nm! 2,5m Ll www.. A wm mmlmmnmnm l! QM :m m 25.5 N b llllllllllll 'QN z. MM? lv. ummzgzou l! WN L .5o ESS NN S MESE w .,w. R mA ml VJ NH I Dl E S o lu ATTORNEY.

REFINING OF CRUDE COKE OVEN LIGHT OIL This invention relates to the treatment of hydrocarbon distillates of an aromatic nature and more particularly refers to a new and improved method of refining coke oven light oil to produce refined distilled aromatic products which pass all nitration grade specifications.

Crude coke oven light oil derived as a product from the destructive distillation of coal consists principally of benzol, toluol and xylol in admixture with unsaturated hydrocarbons such as olefins and dienes together with small amounts of phenol, nitrogen and sulfur organic compounds. Nitration grade `aromatics, particularly nitration grade benzol, derived from crude coke oven light oil must be almost entirely free from these impurities in order to meet the rigid specifications demanded by industry. In recent years, the unsaturated compounds such as coumarone and indene have become more important commercially and of great value. Consequently a process for refining crude coke oven light oil should take into account not only the purification of the aromatic constituents but also the recovery of polymers resulting from the polymerization of `the unsaturated hydrocarbons.

` Conventional methods of refining crude coke oven light oil involve treatment with sulfuric acid to polymerize the unsaturates, neutralization of the acid treated oil with an alkali, and fractionation of the neutral oil to separate the benzol, toluol and xylol components. Probably the most common practice in industry is to treat the crude coke oven light oil with concentrated sulfuric acid, 66 B. or higher, in amount sufficient to polymerize the unsaturates and produce an acid sludge which, upon standing, will settle into a separate layer and is withdrawn. The acidtreated oil is then washed with aqueous alkali to neutralize the oil and the spent alkali separated from the oil. The

neutral oil is then subjected to conventional fractiona-` tion for separation into the individual aromatic components. This practice is extremely disadvantageous by reason of the fact that it produces large quantities of acid sludge which contain valuable polymerized compounds representing not only a great loss of acid, but a loss of polymerized material, the disposal of which is extremely difficult. `Washing the acid-treated oil with aqueous al kali does neutralize the acid constituents in theoil but fails to remove neutral esters of the type formed during the treatment with sulfuric acid which esters decompose on subsequent distillation, yieldngtarry residues and sulfur dioxide, which in turn bring about corrosion trouble not only on distillation apparatus, but also contaminate the aromatic products unless special expensive steps are taken to remove such impurities.

Because ofthe heavy sludge formation when employing strong sulfuric acid, with loss of sulfuric acid and loss in yield of`valuable hydrocarbon constituents, the suggestion was made to use a weaker sulfuric acid, below 66 B., to reduce the amount of sludge formation. `In a few H2504 to 105% rice uncommon instances Where the crude coke oven light oil contains an extremely low amount of impurities, such treatment with dilute sulfuric acid was satisfactory. Unfortunately, with most crude coke oven light oils, the use of dilute acid, while it produced very little or no sludge during the washing process, resulted in an oil containing an appreciable amount of impurities and the resultant products obtained from subsequent fractionation did not pass pure product specications.

In a modified process, as shown by Ingram Patent 1,973,901, the oil is treated with acid and then agitated with water which dilutes the acid and causes some of the acid polymers to dissolve back into the oil. The dilute acid is withdrawn and the oil washed with a large amount of alkaline solution. As pointed out by the patentee, the oil after washing with acid and alkaline solution, contains dispersed sludge which remains in the oil and which subsequently is removed by distillation. However, these sludge particles dispersed in the oil as Well as the sulfuric esters which are formed by acid reaction and not removed from the oil create severe corrosion and contamination problems during the subsequent distillation process. Special precautions are required to minimize these difficulties, as for example, by continuously passing caustic soda solution through the vapor equipment of the distillation unit, with of course, increased cost and operating difficulties.

One object of the persent invention is to provide an efficient, economical process for refining crude coke oven light oil to produce aromatic products meeting nitration grade specifications.

Another object of this invention is to provide an improved method of refining crude coke oven light oil whereby there is removed from the aromatic products corrosive and contaminant constituents prior to fractionation of the aromatic product into separate pure products.

A further object of this invention is to provide an improved method of refining crude coke oven light oil to produce increased yields of aromatic products and increased yields of recoverable polymers.

A still further object of the present invention is to provide an improved method of refining crude coke oven oil without the production of acid sludge and with a recoverable sulfuric acid which can be used for the production of fertilizer acid to manufacture, for example, ammonium sulfate.

Further objects and advantages will be apparent from the following description and drawing.

In accordance with the present invention, refining of crude coke oven light oil may be accomplished by agitating the oil with concentrated sulfuric acid of from 93% H2504 in an amount sufficient to cause polymerization of unsaturates to products of higher boiling point, adding water to the mixture of oil and acid in an amount of about 0.33 to 2.25 volumes of water based on the volume of concentrated sulfuric acid used and agitating the mixture, terminating the agitation and settling the mixture of oil and water until an upper layer of oil and a lower layer of dilute sulfuric acid are formed, spraying water without agitation onto the top surface of the upper layer of oil in an amount of between 0.7 and 1.3 volumes, preferably about l volume, of water based on the volume of concentrated acid. used, retaining the mixture without agitation for a suicient length of time to permit the water to drain down through the upper layer of oil, withdrawing the acid and water, adding an aqueous alkali solution, preferably not in excess of 4% of the volume of the oil and of sufficient concentration to neutralize the acid components in the oil, agitating the mixture of oil and alkali solution, settling the mixture for a sufficient length of time to form an upper layer of neutral oil and a lower layer of alkali solution, withdraw- 3 ing the alkali solution and subjecting the neutral oil to contact with direct steam at a temperature below 250 F. to vaporize aromatic compounds free of corrosive cornpounds as distillate, leaving behind as residue polymer hydrocarbons.

The -accompanying vdrawing is a diagrammatic flow sheet illustrating one vmethod of practicing the invention.

Referring to the drawing, crude coke oven light oil is pumped from storage tank 1 through lines 2 and 3 by means of pump 4 intowasher chamber 5 equipped .with stirrer 6. Washer-chamber 5 maybe a conventional empty chamber with a conical bottom commonly employed in the industry for batch treatment :of oils and usuallyrof .acapacity to-treat from 2500 to 5000 gallons of oilin a single batch. Sincethe crudecoke oven-light oilsfrequently contain small amounts of water, it is desirable to permit the charge oil .to first settle for about minutesafter which time any free water collectingin the bottom of chamber Sis drained'through lines 7 and 3 and sent to the sewer. Concentrated sulfuric acid, 66 B. or higher, yis then charged through line 9 intofchamber 5 and the mixture agitated for about 60 minutes. Ordinarily, 2-.6% of sulfuric acid based on the volume of oil charged, will be adequate for effecting polymerization of the unsaturates in the crude 'coke oven light oil. .A thief sample, as is .common practice .in the art, is taken from the body of oil in chamber 5 and tested for color in the laboratory. If the-results Vshow a color less than 1/2, the oil has been washed suiciently for production of nitration grade benzol having a bromine index number below 15.

Sulfuric acid .functions -in several ways to refine light oil. `The sulfuric acid acts as a catalyst to polymerize certain of the unsaturates converting them to higher molecular weight hydrocarbons which may separate out or which may 'remain in solution in the oil but can be readily separated fromthe oil by distillation due to their higher boiling point. In addition, sulfuric acid acts as a solvent and retains a certain percentage of the hydrocarbons in solution. Further, the sulfuric acid chemically reacts with some of-the hydrocarbon to form esters, a percentage of whichvrernains'in solution in the oil. Sulfuric acid is also an excellent solvent for sulfur compounds, asfor example, mercaptans and thiophenes. In addition, sulfuric acid effects kpartial .removal of nitrogen compounds, as `for example, pyridene type compounds, from the crude coke oven light oil.

After treatment of the crude-coke oven light oil with sulfuric acid followed by settling of the mixture, the sulfuric acid bottom layerseparating out is a sludgy mass containing an appreciable amount .of hydrocarbons. The acid sludge layer as such, is a waste product diicult to dispose of and constitutes a loss of valuable sulfuric acid and lhydrocarbon material. Therefore, water in an amount of approximately 2 volumes of water to the volume of concentrated acid is added through line 11 and the mixture of oil, acid and water agitated for a period of time to obtain intimate contact, say about 30 minutes. Dilution of the acid causes the polymers to dissolve back into the light oil and at the same time claries the suln furie acid making it suitable for use for reaction with ammonia to produce ammonium sulfate. In a few-instances, a small amount of'hydrocarbon polymer mayrbe of such high molecular weight that it is insoluble infboth the light oil and the dilute acid layer and forms a separate layer. This polymer layer, when formed, may, lafter subsequent treatment with water and alkali solution, be withdrawn and utilized as fuel oil. Ordinarily however, little, if any, polymer layer is formed. After the oil, acid and water are thoroughly mixed, the agitation is stopped and the mixture is allowed to settle for at least 60 minutes to form an oil layer, a dilute sulfuric `acid layer and, in some cases, a polymer layer. I have found that even though the mixture of acid, water and oil was permitted to stand for extended periods of time that the oil layer containedrdispersed therein fine particles of acid sludgel and, in addition, contained impurities consisting of nitrogen compounds of the pyridene type. I have discovered that most of these dispersed sludge acid' particles and nitrogen impurities may be removed from the oil layer by spraying water through lines11, 12 and spray 13 onto the surface of the oil layer in an amount roughly equal to l volume of the volume of concentrated acid used. VIt is essential in this second washing with water to avoid agitation of `the `mixture; otherwise there Vis complete failure in separation of the impurities fromthe 'oil layer. I am unable to fully account for the mechanism taking place during the second washing; it appears that'the Water gently seeping down through the body of oil coalesces and carries with it either physically or as a solvent, or both, the iinely dispersed particles of acid sludge and, in addition, has a special solvent effect on the nitrogen compounds so as to cause their removal from the body of oil. In any event, both laboratory and.commercial .operations haveproven that `the addition of -water in the absence of agitation -causes removal `of .impurities which would otherwise be retainedrin the body of oil.

After this .latter water wash, the mixture kis allowedto settle for atleast 30 minutes and the dilute vacid is dischargedfrom the bottom of chamber 5 through lines 7 and 14 Vand sent to :storage for-subsequent use. Remaining in washer chamber 5 is the acid treated oil, kand as previously mentioned, in some cases a vsmall layer of heavy polymer.

The next step in the operation is to neutralize the oil remaining in chamber 5. To accomplish this purpose, an alkaline solution, either sodium hydroxide or ammonium hydroxide, is introduced 'through line '15 into chamber 5. The practice in thepast .has beento employ relatively large amounts of dilutevalkalisolution of -aconcentration of 5% alkali orless, in an attempt to remove additional impurities inthe voil,particularly thesulfuric esters which cause lcorrosion difficulties during subsequent fractionation. Of course, thegreater'the amount of wash liquor employed, thegreater the y,loss of hydrocarbon material. In thepractice of myinvention, I have-found it unnecessary to employ largevolumes of dilute alkali solution and instead, found it `advantageous to utilize as aneutralizing agent, .less .than 4%, preferably 1 3 based Von the volume of oil of a concentrated alkaline solution containing roughly 25% vsodiumfhydroxide or ammonia. The mixture of oil and alkali solution is then agitated foruabout 15-30 minutes, agitation stopped and the mixture allowed to settle for about 30 minutes. The waste alkali is then withdrawn through lines 7 .and 16 and thepolymer layer, if any discharged through lines 7 and 17 tov storage. Neutral washed oil from chamberS is then directedzvia lines 7. and=18 to storage tank.19.

In conventional practice, the neutral oil is sent Adirectly toifractionating units'to distill over thearomatic components such as benzoljtoluol and xylol. During the course of this'fracti'onatiom theincutral oil is heated to `at least 275 Rand inispots attains a considerably higher temperture -due to local overheating. As previously mentioned, there remains in 4solution inthe neutral oil, esters of sulfuric acid which upon heating to a temperature in excess of 250 F., decompose to form tarry sludge and .SO2 gas which corrodes the fractionating equipment and contaminates the product. Furthermore, the high temperatures cause overpolymerization of some of the unsaturates therebydepreciating their-value. .I have found that decomposition of the esters of .sulfuricacid and over- .polymerization of theunsaturatescan be avoided by subjecting the neutral oil,.prior to conventional fractionation,

to the action of `direct steam at a temperature Abelow 250 Q erzogen 'ap plates'. Steam is directed through line` 25 into the bottom of column 24, passing upwardly through the column in direct contact with the oil introduced therein through line 23 and causing the lighter oils, i. e. benzol, toluol and xylol to become vaporized` and to separate from the impurities and higher boiling `constitutents in the light oil. The oil in column 24 is maintained at a temperature below 250 F. The steam vaporization may conveniently be carried out at atmospheric pressure, but if desired, subatmospheric pressure may be employed. The operation of steam still 24 may be conducted in a coutinuous or batch manner.

The benzol, toluol and xylol vapors, together with water vapor, are released from the top of the tower through line 26, cooled and condensed in condenser 27 and then sent through line 28 into separator 29 wherein the condensate separates into an upper layer 31 of reined light oil which is directed through line 32 to storage tank 33 and a lower water layer 34 which is discharged through line 35. A portion of refined light oil layer 31 is returned via lines 36 and 37 by means of pump 38 to the top of column 24 to provide reflux condensate therein and to control the temperature in the top thereof. Residue consisting principally of polymerized material collecting in the bottom of column 24 is sent through line 39 to still residue storage tank 41.

The reiined light oil collected in storage tank 33 is substantially free of corrosive constituents and other impurities, and may then be withdrawn through line 42 and directed by pump 43 through line 44 to conventional fractionating units wherein it is separated into individual components, namely, benzol, toluol and xylol, without any diiculty with respect to corrosion and purity of product.

The following example illustrates one method of carry ing out the invention:

Five thousand gallons of crude coke oven light oil are pumped into an acid washer and allowed to settle minutes, after which time a small amount of free water is removed through the bottom draw-off of the washer. The crude coke oven light oil charge has the following analysis (Engler distillation) 76 C First drop 80 C per cent-.. 5.0 100 C do 86.0 110 C .do 91.0 120 C -do 93.0 130 C do 95.0 140 C do 97.0 147 C Decomposition Two hundred twenty-tive gallons of 66 B. sulfuric acid are added to the light oil in the washer and the mixture agitated for 60 minutes. Thereafter, four hundred fty gallons of water are introduced into the washer and agitation continued for another 30 minutes. The agitation is then stopped and the mixture is allowed to settle for 60 minutes. Two hundred twenty-live gallons of water are sprayed onto the surface of the light oil in the washer while maintaining the oil in a quiescent state and the mixture given a further settling period of 30 minutes. After this is accomplished, the dilute acid is drawn otf to storage. At least 90% of the acid used is recovered at this point. One hundred and twenty gallons of 25% NaOH are added to the oil in the washer and the mixture agitated for 30 minutes; the mixture is then allowed to settle for another 30 minutes, after which time the spent caustic water is withdrawn and the neutral oil dropped to storage. From neutral oil storage, the oil is fed continuously to an intermediate point in a still column and at the same time direct steam is admitted to the bottom of the still column thereby Vaporizing the lighter oils (benzol, toluol and xylol) which are collected as distillate. The residue which includes such resinous materials as paracoumarone, neutral esters and sulfur addition compounds, is withdrawn from the still column. The refined Weight oil vapors, i. e". benzol, toluol and xylol condensate substantially free from impurities is directed to an intermediate storage tank and `then fractionated to separate the refined light oils into its individual components.

Although certain preferred embodiments of the invention have been disclosed for purpose of illustration it will be evident that various changes and moditications may be made therein without departing from the scope and spirit of the invention.

I claim: t

` l. A process for refining crude coke oven light oil and minimizing corrosion of fractionating equipment in which the coke oven light oil is separated into aromatic compounds which comprises agitating the oil without dilution with about 2-6% of concentrated sulfuric acid of at least 93% H2SO4 in an amount suicient to cause polymerization of unsaturates to products of higher boiling point, adding water to the mixture of oil and acid in an amount of about 0.33 to 2.25 volumes of water based on the volume of concentrated sulfuric acid and agitating the mixture, terminating the agitation and settling the mixture of oil, acid and water until an upper layer of oil and a lower layer of dilute sulfuric acid are formed, spraying water while maintaining the body of oil in a quiescent state onto the top surface of the upper layer of oil in an amount between 0.7 and 1.3 volumes of water based on the volume of concentrated acid used, retaining the mixture without agitation for a sufficient length of time to permit the water to drain down through the upper layer of oil, withdrawing the acid and water, adding an aqueous alkali solution in an amount suti'icient to neutralize the acid components in the oil, agitating the mixture of oil and alkali solution, settling the mixture for a sufficient length of time to form an upper layer of neutral oil and a lower layer of alkali solution, and subjecting the neutral oil to contact with steam at a temperature below 250 F. to vaporize from the oil aromatic compounds substantially free of corrosive constituents and separating the aromatic compounds by fractionation into benzol, toluol and xylol.

2. A process for refining crude coke oven light oil and minimizing corrosion of fractionating equipment in which the coke oven light oil is separated into aromatic compounds which comprises agitating the oil without dilution with 2-6% of concentrated sulfuric acid based on the volume of oil charged of from 93% H2804 to H2804, adding about 2 volumes of Water based on the volume of concentrated sulfuric acid used to the mixture of oil and acid and agitating the mixture, terminating the agitation and settling the mixture of oil, acid and water until an upper layer of oil and a lower layer of dilute sulfuric acid are formed, spraying about one volume of water based on the volume of concentrated acid used, onto the top surface of the upper layer of oil while maintaining the oil in a quiescent state, retaining the mixture without agitation for a sufficient length of time to permit the water to drain down through the upper layer of oil, withdrawing the acid and water, adding a strong aqueous alkali solution in an amount not in excess of 4% of the volume of the oil and of suiiicient concentration to neutralize the acid components in the oil, agitating the mixture of oil and alkali solution, settling the mixture for a sutiicient length of time to form an upper layer of neutral oil and a lower layer of alkali solution, withdrawing the alkali solution, subjecting the neutral oil to contact with steam at a temperature below 250 F. to vaporize from the oil aromatic compounds substantially free of corrosive constituents and separating the aromatic compounds by fractionation into benzol, toluol and xylol.

3. Ina process for refining crude coke oven light oil and minimizing corrosion of fractionating equipment in which the coke oven light oil is separated into aromatic compounds involving the steps of agitating the oil without dilution with 246% based on the volume of oil charge of concentrated sulfuric acid' of atleast 93% H2SO4 and then with water,"fol1owet1 by neutralization vof the oil with alkali and subsequent fractionation of the neutral oil, the improvement which ,comprises after agitating with sulfuric acid and water, the step of spraying water onto the top surface of vthe oil while maintaining the oil in a quiescent state' and retaining the mixture Without agitation fora sufficient length :of time to permit the water to drain down through the oil, andthe 'further' step prior to fractionation of subjecting the neutral oil to contact with steam Aat a temperature below 250 F. to

vaporize from the oil aromatic compounds substantially free of corrosiveconstituents and separating the aromatic compounds by 'fractionation into benzol, toluol and xylol.

References Cited in the le of this patent UNITED STATES PATENTS 55,426 Morehouse June 5, 1866 1,759,744 Gard et al. May 20, 1930 1,961,204 Desy June 5, 1934 2,001,899 Blair May 21, 1935 2,398,077 Alspaugh Mar. 26, 1946 

1. A PROCESS FOR REFINING CRUDE COKE OVEN LIGHT OIL AND MINIMIZING CORROSION OF FRACTIONATING EQUIPMENT IN WHICH THE COKE OVEN LIGHT OIL IS SEPARATED INTO WITHOUT COMPOUNDS WHICH COMPRISES AGITATING THE OIL WITHOUT DILUTION WITH ABOUT 2-6% OF CONCENTRATED SULFURIC ACID OF AT LEAST 93% H2SO4 IN AN AMOUNT SUFFICIENT TO CAUSE POLYMERIZATION OF UNSATURATES TO PRODUCTS OF HIGHER BOILING POINT, ADDING WATER TO THE MIXTURE OF OIL AND ACID IN AN AMOUNT OF ABOUT 0.33 TO 2.25 VOLUMES OF WATER BASED ON THE VOLUME OF CONCENTRATED SULFURIC ACID AND AGITATING THE MIXTURE, TERMINATING THE AGITATION AND SETTLING THE MIXTURE OF OIL, ACID AND WATER UNTIL AN UPPER LAYER OF OIL AND A LOWER LAYER OF DILUTE SULFURIC ACID ARE FORMED, SPRAYING WATER WHILE MAINTAINING THE BODY OF OIL IN A QUIESCENT STATE ONTO THE TOP SURFACE OF THE UPPER LAYER OF OIL IN AN AMOUNT BETWEEN 0.7 AND 1.3 VOLUMES OF WATER BASED ON THE VOLUME OF CONCENTRATED ACID USED, RETAINING THE MIXTURE WITHOUT AGITATION FOR A SUFFICIENT LENGTH OF TIME TO PERMIT THE WATER TO DRAIN DOWN THROUGH THE UPPER LAYER OF OIL, WITHDRAWING THE ACID AND WATER, ADDING AN AQUEOUS ALKALI SOLUTION IN AN AMOUNT SUFFFICIENT TO NEUTRALIZE THE ACID COMPONENTS IN THE OIL, AGITATING THE MIXTURE OF OIL AND ALKALI SOLUTION, SETTLING THE MIXTURE FOR A SUFFICIENT LENGTH OF TIME TO FORM AN UPPER LAYER OF NEUTRAL OIL AND A LOWER LAYER OF ALKALI SOLUTION, AND SUBJECTING THE NEUTRAL OIL TO CONTACT WITH STEAM AT A TEMPERATURE BELOW 250* F. TO VAPORIZE FROM THE OIL AROMATIC COMPOUNDS SUBSTANTIALLY FREE OF CORROSIVE CONSTITUENTS AND SEPARATING THE AROMATIC COMPOUNDS BY FRACTIONATION INTO BENZOL, TOLYOL AND XYLOL. 